Currently, urban railway vehicles generally run with fixed formation, mainly including 6-car formation and 8-car formation. Running with fixed formation cannot meet flexible requirements of passenger flow volume. If vehicles are designed to have small formation, such as 3-car formation or 4-car formation, and the vehicles run with the fixed formation of 3-car or 4-car in a case of a small passenger flow volume and run with 2 or 3 coupled trains of 3-car formation or 4-car formation in a case of a large passenger flow volume, flexible requirements of passenger flow volume can be met to save power and costs.
In conventional technology, coupling of trains is commonly implemented as coupling at a fixed end. The coupling at a fixed end means that a head end of a train can only be coupled with a tail end of another train, which is inconvenient and time-consuming for coupling the trains.
Coupling at a random end is more convenient than the coupling at a fixed end in implementation. The coupling at a random end means that either ends of a train can be coupled with either ends of another train, which is convenient and time-saving for coupling the trains. However, it is difficult to design a control circuit for coupling at a random end. Therefore, it is desired to provide a switching circuit with which coupling at a random end of a train can be implemented.